Post-grouted piles, as a foundation form for large-span and large-scale structures on calcareous sand, are expected to provide a high bearing capacity, but research on the response of post-grouted piles subjected to axial load in calcareous sand is still in the exploratory stage. In this paper, a model test is constructed for static pressure piles in calcareous sand under axial loading. The response of axial compressive piles, with and without post-grouting, in calcareous sand were investigated, and the test results were compared with those of axial compressive piles, with and without post-grouting, in siliceous sand. The influence of post-side-grouting on the response of a single pile subjected to axial compressive load in calcareous sand and its bearing mechanism were further analyzed. The results show that the change in shaft resistance, caused by the lateral extrusion of calcareous sand, is less than the negative effect caused by particle breakage during pile driving, so single piles without post-grouting in calcareous sand exhibit weaker axial bearing behavior than that in siliceous sand. A single pile with post-side-grouting in calcareous sand can provide a higher bearing capacity by increasing the shaft resistance and tip resistance compared with a single pile without post-side-grouting, and the increased ratio of the bearing capacity of piles, after grouting in calcareous sand, is better than that of piles in siliceous sand. Post-side-grouting can not only strengthen the surrounding soil by the solidification effect of injected cement grout, but it can also have a strengthening effect on the tip resistance. In addition, ideal-geometry grouting has more obvious advantages in improving the bearing behavior of pile foundations than annular point grouting, and higher stability in improving the bearing properties of pile foundations is evident for ideal-geometry grouting. Therefore, it is suggested that a directional grouting device should be adopted in actual projects in the future to form a more stable pile-soil interaction system and to expand the application prospect of pile foundations in calcareous sand.

The traditional design method for drilled shafts rarely considers the influence of construction effect and tip resistance on side resistance, and lacks attempts to improve the performance of drilled shafts without increasing drilled shafts sizing, economic costs and carbon emissions. In this paper, the influences of construction-effect and shaft tip resistance on the side resistance of large-diameter drilled shafts before and after combined grouting were studied by full-scale field tests. The reinforcing effect of combined grouting on bearing capacity was confirmed, and the potential of applying combined grouting to realize sustainable development, the economy, and environmental protection was introduced. The mechanisms of softening-effect and reinforcing-effect on the side resistance of large-diameter drilled shaft are discussed in depth. The field test results showed that the construction-effect and shaft tip sediments caused the side resistance to soften, and the lower the shaft tip resistance, the more serious the side resistance softening-effect. The mobilization of side resistance was affected by the soil strength underneath the shaft tip. The shaft tip bearing capacity was improved after sediment compression, which helped to reinforce the side resistance near the shaft tip. Combined grouting improved the side resistance reinforcing-effect even further and broadened the range of soil layers that can benefit from it. The fundamental reason influencing the side resistance softening-effect and reinforcing-effect of the drilled shaft was the change in soil radial effective stress. This research provided certain references for improving the performance of drilled shafts without increasing drilled shafts sizing, economic costs and carbon emissions.

The artificial ground freezing method has been widely used in shield tunneling breakthrough working shafts. The freezing effect was mainly considered in the previous research, and the heat generation of the shield machine was not considered, which has great influence in actual engineering. In this paper, a coupling calculation model, considering phase change latent heat, is establishes that by containing the freezing process and heat generation of the shield machine, the model is verified. A numerical simulation is carried out for several working conditions that may occur in actual projects, and the following conclusions are obtained. Although the heat dissipated by the normal tunneling of the shield machine will melt the frozen soil curtain that originally meets the design requirements, the thickness of the frozen soil curtain after melting cannot reach the initial design, though it is still within the safe range. In the process of a continuous rotation working condition, the bottom and sides of a cup-shaped frozen soil curtain are partially melted in the early 6 day stay of the shield machine, and the thickness is reduced to a relatively stable value of 0.8 m. In a temporary shutdown working condition, when the contact surface temperature between the shield machine shell and the frozen soil drops to −12 °C after almost 4 days of shutdown, the shield machine may not keep tunneling forward due to the freezing effect. The research results will benefit the freezing design and management of the shield tunneling breakthrough working shaft under extreme conditions.